Established lines of pituitary cells (GH cells) will be utilized to further explore post-receptor mechanisms of thyrotropin-releasing hormone action. Specifically, experiments are proposed to determine relative contributions of cyclic nucleotides and Ca ions as intracellular mediators of TRH action on secretory events. Techniques have been developed with whicH the isolation of GH cell variants altered in cyclic AMP action will be attempted. In addition, studies of Ca ions dependent and cyclic AMP-dependent pathways of protein phosphorylation will be compared with TRH-induced alterations. We will explore potential ionic dependence of TRH stimulation of secretion and study direct effects of TRH on Ca ions metabolism. These studies are directed toward further clarifying the cellular basis of TRH action.